A permanent magnet synchronous machine running directly on the network requires a traditional synchronous machine type damper winding for the rotor. Preferably, the damper winding is manufactured from copper.
In a traditional synchronous machine, the bars of the damper winding and the short-circuiting ring are typically soldered together. Soldering requires a significant degree of heat input to the soldered site. Since copper conducts heat very well, it is effectively transferred to the rotor. In the case of manufacturing a rotor for a traditional synchronous machine, that is not a problem.
However, the permanent magnets in a permanent magnet synchronous machine do not withstand high temperatures; instead, the temperature in this type of almost open magnetic circuit must be kept below 100° C. Therefore, the joint between the copper bars of the damper winding and the copper short-circuiting ring is to be provided in another manner.
Welding is a better jointing method than soldering for copper parts for the reason that it is quicker and the necessary quantity of heat is lower. However, if the short-circuiting ring and a bar of the damper winding were welded directly together, heat would be conducted to the permanent magnets to such extent as to destroy them.